Shrub diseases exist in a vast array of varieties--from fungal infections to bacterial problems and pest diseases--which can cause cosmetic damage or possibly lead to plant death. No matter the problem, there is an arsenal of ready-to-choose agents that will clear up the problem. Both organic and chemical options are available, depending upon your preference.
Organic oils are widely used to treat shrub diseases. Horticultural oil is a petroleum-based product that has been refined into a mineral oil and mixed with a secondary agent that allows water and oil to mix for application capabilities on plants. For safe treatment, only apply horticultural oil to plants if temperatures fall between 40 and 90 degrees Fahrenheit. This type of oil often treats powdery mildew on shrubs. Neem oil comes from the neem tree (Azadirachta indica). Oil is extracted from the neem tree's fruit and seeds and is used as treatment of pest diseases such as that caused by aphids, according to the Purdue University Extension.
Sulfur-based products have been used for thousands of years as organic fungicides, according to the Purdue University Extension. Sulfur inhibits the growth of fungal spores that cause infections on shrubs, such as rose black spot and rust. They are available in dust, liquid or powder form. Do not mix sulfur fungicides with oils. Additionally, only use sulfur products in temperatures below 80 degrees Fahrenheit to avoid plant injury.
Copper fungicides are organic products for shrub diseases. They often treat fungi as well as bacterial infections, including downy mildew and bacterial leaf spot, according to the Purdue University Extension. A mixture of the fungicide copper sulfate with lime brings the pH level from acid to neutral and makes copper effective against bacteria as well as fungi, making copper a safer product for use on plants. However, the acidity of copper sulfate may cause injury.
Chemical products are inorganic, created from man-made ingredients and are generally applied to shrubs every one to two weeks, depending on the particular problem. Some chemical fungicides are applied as a preventive measure--to prevent disease--while others are used to cure an existing problem. Products with an active ingredient, such as mancozeb, chlorothalonil or myclobutanil, for example, usually come in spray form and successfully treat shrub diseases such as fungal leaf spots, according to the Clemson University Extension.